Breeding groups of talapoin and patas monkeys are housed in large runs. Regular quantitative records of social behaviour in the groups are made, and reproductive status of the females is followed closely. In the case of the patas, which have no external signs of cyclic activity, vaginal smears and lavages are used. The object is to correlate changes in social interaction patterns with female reproductive cycles. Three types of cycle are considered: the menstrual cycle; the cycle of mating, pregnancy, and lactation; and the mating season-non mating-season cycle, which happens to be especially clear in these two species in the wild and under my conditions. Detailed analysis of changes in the vaginal cell population during these cycles is also being made. Changes in interaction patterns associated with adolescence are being followed, in relation to the developing cyclicity of the females especially. These are the sixth and seventh species studied in a long term comparative study of social organization as it relates to reproductive cyclicity, and I hope to be able to relate present findings to those already published in terms of evolutionary and adaptation to environments within the Old World monkeys.